Elsevier

Cognition

Volume 122, Issue 1, January 2012, Pages 37-50
Cognition

Escaping capture: Bilingualism modulates distraction from working memory

https://doi.org/10.1016/j.cognition.2011.08.002Get rights and content

Abstract

We ask whether bilingualism aids cognitive control over the inadvertent guidance of visual attention from working memory and from bottom-up cueing. We compare highly-proficient Catalan–Spanish bilinguals with Spanish monolinguals in three visual search conditions. In the working memory (WM) condition, attention was driven in a top-down fashion by irrelevant objects held in WM. In the Identify condition, attention was driven in a bottom-up fashion by visual priming. In the Singleton condition, attention was driven in a bottom-up fashion by including a unique distracting object in the search array. The results showed that bilinguals were overall faster than monolinguals in the three conditions, replicating previous findings that bilinguals can be more efficient than monolinguals in the deployment of attention. Interestingly, bilinguals were less captured by irrelevant information held in WM but were equally affected by visual priming and unique singletons in the search displays. These observations suggest that bilingualism aids top-down WM-mediated guidance of attention, facilitating processes that keep separate representations in WM from representations that guide visual attention. In contrast, bottom-up attentional capture by salient yet unrelated input operates similarly in bilinguals and monolinguals.

Highlights

► Bilinguals and monolinguals compared in three different versions of a visual search task. ► Working memory (WM) version: attention driven in a top-down fashion by irrelevant objects held in WM. ► Identify condition: attention driven in a bottom-up fashion by visual priming. ► Singleton condition: attention driven in a bottom-up fashion by a unique distracting object. ► Bilinguals less captured by irrelevant information held in WM but equally affected by visual priming and unique singletons.

Introduction

It has been repeatedly shown that bilingualism has an impact on cognitive control mechanisms required to resolve conflicting responses to stimuli – as in Stroop-like tasks (e.g. Bialystok and Martin, 2004, Carlson and Meltzoff, 2008, Costa et al., 2009, Costa et al., 2008, Hernández et al., 2010, Martin-Rhee and Bialystok, 2008). This impact has been indexed by two effects. First, conflict effects produced by incongruent information are larger for monolinguals than for bilinguals (e.g., Bialystok et al., 2004, Bialystok et al., 2008, Costa et al., 2008, Costa et al., 2009, Hernández et al., 2010, Hernández et al., 2010). Reduced conflict effects have been taken as evidence that bilingualism could benefit inhibitory mechanisms required to overcome conflicting information. Second, bilinguals are overall faster than monolinguals (e.g., Bialystok, 2006, Costa et al., 2008, Costa et al., 2009, Martin-Rhee and Bialystok, 2008). This observation has been interpreted as evidence that bilinguals are more efficient at adjusting behaviour according to the current demands. Thus, in the case of tasks involving conflicting information, bilinguals can alternate more easily than monolinguals between trials that require conflict resolution and those that are free of conflict (see Costa et al., 2009).

These bilingual advantages have been associated with the use of control mechanisms that prevent linguistic interference during bilingual language processing. Although the specific language control mechanisms at play are still under debate [inhibition of the unintended language (e.g. Green, 1998) vs. selection of the intended language (e.g. Costa, Santesteban, & Ivanova, 2006)], it has been argued that these mechanisms partially overlap, functionally and anatomically, with general cognitive control mechanisms (Abutalebi and Green, 2007, Abutalebi and Green, 2008). As a result of this, bilinguals may engage general mechanisms of cognitive control (e.g., inhibitory processes, task monitoring) more frequently than monolinguals, giving rise to the bilingual advantage in control processes.

Recent studies have extended the bilingual advantage to other cognitive control processes that do not seem to involve conflict resolution, such as dual modality monitoring (Bialystok, Craik, & Ruocco, 2006), reactive inhibition (Colzato et al., 2008), and task-switching (Prior & MacWhinney, 2010). These findings raise the question of the boundaries for the effects of bilingualism on general-domain cognitive control.

In the present study we explored these boundary conditions by examining the effects of bilingualism on particular bottom-up and top-down factors that modulate visual search. In the remains of the Introduction, we provide a description of the top-down and bottom-up phenomena of attentional guidance, followed by our predictions on the impact that bilingualism would have on them.

The ability to guide attention to a target object can be affected by distracting stimuli that are either highly salient relative to the other elements present (bottom-up guidance; e.g. Theeuwes, 1991, Theeuwes, 1992, Theeuwes et al., 2003) or that match items held in working memory (WM) (top-down guidance; e.g. Downing, 2000, Soto et al., 2005, Soto and Humphreys, 2009). For example, when driving your car, your attention can be captured by signals indicating certain directions with similar names to the one you have in mind (top-down guidance). However, your attention is also captured by salient stimuli such as the sound of an ambulance or the red lights indicating sudden braking of the car just in front of you (bottom-up guidance).

Experimental studies of bottom-up guidance of attention have often used the phenomenon of singleton capture. As example of this task, and highly relevant for our study, Theeuwes et al. (2003) found that visual search is disrupted by the concurrent presence of distracting stimuli that are unique in some irrelevant dimensions (i.e. singletons). In these Singleton paradigms, participants are presented with a search display composed of coloured geometrical figures, each containing a line. All lines are totally straight (distracters), except for one that is slightly tilted towards the left or the right (the target). Participants’ task consists in looking for the tilted line and indicating its direction via button press (right or left), as fast as possible. That is, the shapes and colours of the geometrical figures are completely irrelevant for the task at hand, and participants only have to ignore them. The crucial aspect of this paradigm is the inclusion of so-called singletons, namely a figure that outstands among the rest in the display. Neither the shape nor the colour of this singleton figure is repeated in any other figure, which makes the singleton perceptually salient in the display search (see Fig. 1C in Section 2 for a schematic illustration of the Singleton version of our paradigm). The perceptual saliency of the singleton makes it hard for participants to prevent this item from capturing attention during visual search. In fact, performance is facilitated (Singleton benefit) when the target line falls within the singleton figure, and disrupted (Singleton cost) when the target line falls within any other figure of the display (relative to a neutral condition where no singleton figure is present in the search display).

Effects of top-down guidance have been demonstrated in studies examining how information actively maintained in WM affects attentional guidance. Soto et al. (2005) found that visual search performance is affected by the concurrent presence of distracters that match the contents of stimuli held (WM). As in Singleton paradigms, Soto et al.’s participants were instructed to look for the tilted line (target) among all the lines inside each coloured geometrical figure in the search display. Prior to be presented with the search display, however, participants had to memorize a coloured figure (the cue) and maintain it in WM for a memory test, which came immediately after the visual search task. That is, participants were first presented with a to-be-memorized cue. Then, the search display appeared and they had to search for the tilted line. Subsequently, participants were presented with a single figure and asked whether it matched both the colour and shape as the cue they were keeping in WM.

The crucial manipulation is whether the target line falls within an irrelevant coloured figure that corresponds to the cue kept in WM. If the cue kept in WM contains the target line, performance is facilitated (a WM benefit); however if the cue does not contain the target line then performance is disrupted (a WM cost) (performance is in both cases compared against a neutral condition in which the cue held in WM is not present in the search display) (see Fig. 1A in Section 2 for a schematic illustration of the WM version of our paradigm).

Importantly, these effects are very much reduced when the cue presented prior to the visual search display does not need to be kept in WM. In the so-called Identify paradigm, participants are presented with exactly the same cues and search displays as in the WM paradigm, but they are not asked to keep the cue in WM. For example, they may be asked to compare the colour and shape of two initial visual cues presented consecutively within a short period of time. The search task is carried out if the cues match (as in the WM condition), otherwise no response is made (e.g., Soto and Humphreys, 2009, Soto et al., 2007, Soto et al., 2005) (see Fig. 1B in Section 2 for a schematic illustration of the Identify version of our paradigm).

Since the effects of the cue are greater in the WM paradigm compared with the Identify paradigm, it can be concluded that there is top-down WM-based cueing in addition to any effects based on bottom-up visual priming (e.g., Hernández et al., 2010, Soto et al., 2007).

The main goal of our study is to explore to what extent bilingualism has an impact on the top-down and bottom-up control of attentional guidance.

We hypothesize that bilingualism may have an impact on the top-down processes involved in guidance of attention. This hypothesis is based on the cognitive consequences of the extra processes that bilingualism exerts during language processing. There is agreement that the two languages of a bilingual are simultaneously activated, both during speech production (e.g., Colomé, 2001, Costa and Caramazza, 1999, Costa et al., 1999, Green, 1998, Hermans et al., 1998, Kroll et al., 2006) and comprehension (e.g., Spivey and Marian, 1999, Van Heuven et al., 1998). In the case of bilingual speech production, the utterance is conceptually-driven. That is, the speaker has to map a thought (i.e., the concept of table) onto the lexical items of the intended language. However, the concept may activate the lexical forms of more than one language (e.g., both table and mesa [the Spanish word for table]). This means that bilinguals need to override distraction from the irrelevant lexical form (e.g., mesa), in order to avoid miss-selection of the lexical item and a consequent language intrusion. A similar process is imposed by bilingual language comprehension. Although in this case language processing is initiated by perceptually-driven mechanisms (i.e., recognizing spoken or written words), the lexical forms of the two languages may again be simultaneously activated. That is, accessing a concept through a written or spoken word in either language may automatically activate the lexical form of the other language too. This means that the bilingual speaker needs to apply top-down mechanisms of control during language comprehension to focus on one set of lexical representations (i.e., language A) and not the other (e.g., language B). The simultaneous activation of the two lexical forms during both bilingual language production and comprehension leads us to hypothesize that bilingual speakers may need to develop strong mechanisms of top-down guidance to keep focused on the current goal (language A) while avoiding capture from the active representations of the unintended language (language B). This hypothesis proposes that, relative to monolinguals’, bilinguals’ language processing places extra demands on top-down control. In turn this may lead to bilingual participants having a generally better ability to modulate any top-down directing of attention, in our case to avoid distraction from irrelevant information.

To test this hypothesis we compared the performance of bilinguals and monolinguals in a version of the WM paradigm of visual guidance of attention used by Soto et al. (2005) – (Experiment 1a – WM condition). If indeed bilinguals have a more efficient top-down mechanism of attentional guidance, then their search performance should be less affected by the contents of WM, when compared to monolingual individuals. Note though that, since many of the components of the EC system are not well-understood, it is still unclear which specific top-down WM-mediated mechanisms are used to guide attention. Thus, we cannot more precisely predict which particular top-down mechanisms of attentional control are affected by bilingualism. Even so, we note that several authors have suggested that one mechanism of attentional control may be to compartmentalize items in WM, so only the most relevant items (i.e., the search target and not the memory stimulus, in our paradigm) gain control of behaviour by accessing WM (see Olivers, 2009). This compartmentalization process may be modulated through frontal lobe structures (Soto, Humphreys, & Heinke, 2006). From this it can be predicted that search in bilingual participants would be more guided by the task-relevant target and less by irrelevant items in WM, compared with monolingual individuals. This hypothesis also makes interesting predictions about the two main effects observed in the visual search task (WM costs and benefits).

The reduced effect of irrelevant information in WM on search in bilingual participants should, in principle, be indexed by a reduction in the magnitude of the WM cost and WM benefit for bilinguals as compared to monolinguals. That is, whatever the effects of the item held in WM (e.g., whether it helps or hinders target detection, on valid and invalid trials), the effect should be reduced in the case of bilinguals since their visual search performance would be less affected by the memory item. Importantly, however, a reduction of the WM benefit for bilinguals may be much more informative than a reduction of the WM cost. This is because the WM cost involves at least two different components: attentional capture from the cue held in WM, and redirection of attention to the correct figure where the target is located (see Soto et al., 2006, for neuropsychological evidence on the effects of frontal lobe damage on impaired redirection of attention on invalid trials). In contrast, the WM benefit is more likely to reflect the initial directing of attention, given that participants would not need to further reallocate their attention on valid cue trials, since the target is already inside the attended figure.

These predictions make clear that one can find experimental situations in which the increased control of attention in bilingual individuals is translated into worse performance in the task – in this case with the benefits from valid cueing being reduced. Note that, there are other studies showing that better attentional processing in bilinguals may lead to a disadvantage under certain experimental conditions. Take the attentional blink (AB) paradigm. There is evidence that a deeper engagement of attention in the processing of a first target can result in a more pronounced AB for a second target (e.g., Olivers & Nieuwenhuis, 2005). Consistent with bilinguals showing deeper engagement of attention, Colzato et al. (2008) showed that bilingual participants had a larger AB than monolingual participants.

To ensure that any results in the WM paradigm reflect WM and not bottom-up priming, we also compared the performance of bilinguals and monolinguals in a version of the Identify paradigm used by Soto et al. (2005) – (Experiment 1b – Identify condition). In this condition participants identified the initial coloured figure (the cue) presented on each trial, but they did not have to hold it in memory (see above). If the better attentional control of bilingual participants is shown primarily when attention is directed through WM, not when it is cued in a more bottom-up fashion, then we expect that the effects of the cue would be comparable between bilinguals and monolinguals in the Identify condition. This result would rule out the possibility that the effect of bilingualism in the WM condition is due to contrasting effects of visual priming between bilinguals and monolinguals.

Before discussing the bottom-up processes, it is important to note that the aim of the current investigation is not to compare bilinguals and monolinguals in WM capacity, but rather to assess differences in WM-based control of attention. That is, we will examine whether bilingual performance in visual search is affected by the item held in WM to a lesser extent than monolingual performance.

To asses whether bilingualism has any impact on the bottom-up guidance of attention we used a version of the attentional guidance paradigm described above (Theeuwes et al., 2003). This visual search task consists in finding the only tilted line present in a display. Distracters consisted in a “singleton” item – one of the geometrical coloured figures in the display that was unique in colour and shape relative to the other figures (see above). As with top-down cueing from WM, singleton costs and benefits can be distinguished according to whether the singleton contains the target line (tilted line; benefit) or a distracter line (a straight line; cost) – (relative to the neutral baseline). Following the same logic developed when drawing hypotheses about the bilingual effect in the WM condition, bilingual modulation of the Singleton benefit would clearly indicate that bilingualism has an impact on bottom-up attentional guidance. Bilingual modulation of the Singleton cost, however, could be attributed to bilingual advantages in either bottom-up attentional guidance or to more efficient attentional disengagement and redirection. Thus, similarly to what happens in the WM condition, Singleton benefits rather than Singleton costs are more likely to reflect the initial directing of attention.

When assessing whether bilingualism has an effect on bottom-up processes, one could think that this issue is already known given that bilingualism has been found to have an effect in tasks where conflicting distracters are generally processed in a bottom-up fashion. However, we believe that such studies cannot be taken as definite indication that bilingualism affects bottom-up guidance of attention. Consider for example the flanker task, in which incongruent trials contain flanker arrows pointing in the opposite direction (distracters) to a central target (e.g., ←←→←←). These distracters lead to conflict by eliciting the opposite response (left) to the target (right). As a consequence, cognitive control mechanisms need to be put at play to suppress the conflicting information provided by the flankers. Although such conflict effects arise through bottom-up processing of the distracters, we cannot determine whether the reduced conflict effects shown by bilingual participants arise because bilinguals have reduced capture by the flankers (a bottom-up account) or because bilingual individuals can effect better control over the subsequent conflict (a top-down account).

Alongside differences in the control of attention, bilinguals may also show general improvements in performance relative to monolingual participants. As described above, an overall advantage for bilinguals has been observed in Stroop-like tasks (e.g., Bialystok, 2006, Costa et al., 2008, Costa et al., 2009, Martin-Rhee and Bialystok, 2008), and this has been interpreted in terms of a more efficient monitoring system (e.g., Costa et al., 2009). Monitoring can be thought to reflect the ability of the cognitive system to calibrate itself to deal with specific task-demands through appropriate adjustments (e.g., engaging inhibitory processes). For example, in a Stroop-like context, this self calibration can be achieved on the basis of an assessment of current demands by extracting an abstract index of conflict. On the basis of the computed trial-by-trial conflict, the monitoring system may trigger cognitive control processes (e.g., the prefrontal cortex in case of inhibition) to intervene and adjust processing according to the current demands (e.g., Botvinik, Braver, Barch, Carter, & Cohen, 2001). In this scenario, a bilingual advantage in overall speed may arise in any task engaging the monitoring system. Note that similar monitoring processes may be involved here, perhaps adjusting WM control according to cue validity. Whether the overall differences in processing speed, reflecting this monitoring process, modulate the effects of (both top-down and bottom-up) attentional capture can be assessed by evaluating how cue validity effects in bilingual and monolingual participants vary across processing time. For example, if differences in overall reaction time (RT) reflect changes in a general parameter, then the cue validity effects may be relatively independent of differences in RT distributions across participants. This was tested here (Costa et al., 2009).

To recapitulate, we examined the ability to control attention in bilingual and monolingual participants under conditions of cueing from irrelevant stimuli in WM, bottom-up visual priming, and singleton distraction. We expected to find an overall RT difference between monolinguals and bilinguals in all the three paradigms (WM, Singleton and Identify). However, if bilingualism specifically modulates top-down attentional guidance,1 then differences in the magnitude of the cue validity effects (and especially in the benefits from valid cueing) will be present only in the WM paradigm.

Section snippets

Participants

Eighty participants (40 bilinguals, 40 monolinguals) took part in the WM and bottom-up Singleton conditions in a counterbalanced order during the same testing session, and another 80 different participants (40 bilinguals and 40 monolinguals), took part in the bottom-up Identify condition. Several steps were taken to guarantee that the bilingual and monolingual samples were comparable. First, all of the participants were from the same country and they were raised in the same social, cultural and

Data analysis

In order to address the predictions put forward in the Introduction about the effects of bilingualism on visual guidance of attention, we conducted separate analyses for each of the three conditions (WM – Section 4.1, Identify – Section 4.2, and Singleton – Section 4.3). In these analyses we took error rates and reaction times as dependent variables, “Type of Trial” (valid, neutral, invalid) as a within-subjects factor, and “Group” (bilingual, monolingual) as a between-subjects factor. In all

Results

Trials with errors were excluded from the RT analyses (no main effects or interactions were found in the analyses of errors; all Ps > .16). RTs that were greater than 2.5 SDs from the mean were also excluded. This last action led to the loss of fewer than 2.7% (bilinguals) and 2% (monolinguals) of the trials in the WM condition, 1.8% (bilinguals) and 2% (monolinguals) of the trials in the Identify condition, and 5% (bilinguals) and 3.2% (monolinguals) of the trials in the Singleton condition.

General discussion

In this study we aimed to test the hypothesis that bilinguals would develop strong top-down mechanisms of attentional control as a result of constantly having to handle top-down sources of distraction, namely, activation from lexical representations in the unintended language. Thus, in the present context, bilinguals would experience less influence than monolinguals from irrelevant information that guides attention in a top-down fashion from WM. In contrast, bottom-up guidance of attention

Acknowledgments

This research was supported by two grants from the Spanish Government (PSI2008-01191/PSIC & Consolider Ingenio 2010 CE-CSD2007-00121/SGR “2009-1521) and by grants from two UK research councils (BBSRC and MRC). Mireia Hernández was supported by a Pre-doctoral fellowship from the Catalan Government (SGR-2005). Mireia Hernández is now at Center for Brain/Mind Sciences (CIMeC), University of Trento (Trento, Italy). We thank Jan Decock, Sara Rodríguez, and Violeta Pina for their assistance during

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